Kemper has written several sketch comedy shows[6] many of them with her comedy partner Scott Eckert,[3] a fellow Princeton grad.[2]

Kemper is a contributing writer for the national satirical newspaper The Onion[7] and for McSweeney's, the literary journal founded by Dave Eggers.[3] Her essays for McSweeney's included "Listen, Kid, The Biggest Thing You've Got Going For You Is Your Rack",[8] "Following My Creative Writing Teacher's Advice To Write 'Like My Parents Are Dead'",[9] and "Some Relatively Recent College Grads Discuss Their Maids".[10] She is also a contributor to The Huffington Post,[11] the liberal American news website founded by Arianna Huffington. Pieces include "I'm Not Exactly Afraid of Really Intense Fashion".[12]

Kemper has also appeared in several national commercials. One was a radio spot for Dunkin' Donuts.[3] In a commercial for KMart, Kemper is featured as a camper with a live tarantula crawling over her face.[13]
I'm the most comfortable when I'm playing a naturalistic character. I auditioned for Saturday Night Live, and when I was doing the biggest characters, I felt the least comfortable. I'm just more comfortable when it's some version of myself.
“”Ellie Kemper[14]Upon moving to New York City, Kemper participated in the People’s Improv Theatre[2] and the city troupe of Upright Citizens Brigade, an improvisational comedy and sketch comedy theater. She has appeared in several shows for the Brigade, including Death and/or Despair, Listen Kid, Gang Bang and The Improvised Mystery.[3] At the UCB, she performed with the house improv teams Mailer Daemon and fwand.[3] At the PIT, she performs with the house improv team Big Black Car.[15] In August 2008, she auditioned for a spot on the NBC sketch comedy show Saturday Night Live, but was not cast.[14] In July 2009, Kemper was named one of Variety magazine's "10 Comics To Watch".[14] Big Black Car teammate Kristen Schaal was also named.

Kemper gained some Internet fame in August 2007 for her part in "Blowjob Girl", a humor video on the sketch comedy site Derrick Comedy. The video, which was circulated on the popular site CollegeHumor, was a two-minute close-up of Kemper offering to perform oral sex on her boyfriend, but startling him by promising to bite and smash his genitals, which she seems to believe is arousing.[17] As of October 2010, the video has been viewed more than 17.6 million times on YouTube.[18] Kemper said in an April 2010 interview with The A.V. Club that "It’s just one video in a sea of many."[19] Kemper has also contributed an article to CollegeHumor entitled "Regarding Our Decision Never To See Me Again."[20] She also had a minor role in the 2009 movie Mystery Team.

She also co-starred in the fake iPhone commercial on Late Night With Conan O'Brien in January 2007, six months before the first iPhone was released by Apple Inc.[21]

Being on set with them is like being in a dream, except the dream is real and I can reach out and touch them. Except I am trying not to touch them too much, because I was raised right.
“”Ellie Kemper, on The Office[2]Kemper auditioned for a role in Parks and Recreation, an NBC comedy series started in 2009 by Michael Schur and Greg Daniels, creator of the series The Office. She was not cast in the role, but received a call back to audition for a supporting role in The Office as Erin Hannon, a secretary filling in for the regular secretary Pam Beesly when she briefly left the job at the end of the fifth season. Kemper was cast in the role, and started appearing in the show in April 2009. The character was originally written to be more sarcastic and dry, but the writers changed her to be more perky and optimistic to more closely resemble Kemper herself. Kemper described the character as "an exaggerated version of myself".[1] Kemper described herself as a "huge fan" of the show and was thrilled to be on the show.[2] Although the character was originally intended for 4 episodes, the producers were impressed with Kemper and signed her as a regular in the sixth season.[1]Jennifer Celotta, a screenwriter with the series, described Kemper as a "fun addition" to the show.[23]

Kemper received positive reviews for her role in The Office. Alan Sepinwall, television columnist with The Star-Ledger, praised the "infectious joy and sweetness" she brought to the show.[1] Joshua Ostroff of Eye Weekly described Erin as one of the best new television characters of the 2008-2009 season and said, "Erin’s high-grade adorability, up-for-anything attitude and sheer niceness is unlike anyone else in the office, adding a welcome new wrinkle for next season."[24] Andy Shaw of TV Fodder said she "adds some freshness to the cast"[25] and Josh McAuliffe of The Times-Tribune in Scranton, Pennsylvania, said he liked Erin's "cheerful, appealingly goofy personality".[26] In October 2009, Kemper appeared in Subtle Sexuality, a set of three Office webisodes about efforts by Erin and Kelly Kapoor (Mindy Kaling) to start a girl group.[1]